The present invention relates to a method and device for detecting hydrogen peroxide.
There are many applications in which it is desirable to measure hydrogen peroxide concentration. For example in the food industry hydrogen peroxide is used to sterilize metal cans for can food preparation. Ensuring a proper application of the hydrogen peroxide to such cans is critical to maintaining proper food safety. Hydrogen peroxide is also used as a chemical disinfection agent for sterile rooms. Most importantly, hydrogen peroxide is used to sterilize industrial and medical devices. In such application, hydrogen peroxide may be applied as a liquid solution or preferably as a vapor. Hydrogen peroxide vapor may be combined with the application of a plasma field. Such systems are more fully described in U.S. Pat. Nos. 4,643,876 and 4,756,882 which are incorporated herein by reference. One such commercially available system is the STERRAD(copyright) brand sterilizer from Advanced Sterilization Products of Irvine, Calif.
In the STERRAD and similar systems, instruments to be sterilized are typically first cleaned, dried and then encased in a bacteria-proof, vapor transmisive envelope such as a TYVEK(copyright) (spun bonded olefin)/MYLAR (polyester film) pouch or central supply room wrap (CSR wrap). The instruments are placed into a sterilization chamber and gas within the chamber is evacuated to place the chamber at a vacuum pressure. Hydrogen peroxide vapor enters the chamber, and contacts the instruments to sterilize them. Power added through electromagnetic radiation or other means creates a plasma of the hydrogen peroxide, preferably at the end of the cycle. After the energy source used to create the plasma is removed, the plasma ions recombine to form oxygen and water.
The sterilization process may be checked in several ways. For instance, biological indicators may be placed in various locations through out the sterilization chamber to evaluate the sterilization process. A typical biological indicator is shown in U.S. Pat. No. 5,552,320 to Smith, incorporated herein by reference. In general, a biological indicator contains a known quantity of a living test organism. After the sterilization procedure, the organism is cultured to see whether any of the test organisms have survived the sterilization procedure. Such a culturing process necessarily entails a time delay, usually a day or more.
An alternative method of checking the operation of the sterilization cycle is to test for the presence and amount of hydrogen peroxide vapor within the sterilization chamber. If the desired amount of hydrogen peroxide is reached within the chamber, one can at least assume that the sterilization device is functioning as intended. The evaluation should preferably be instantaneous so that if a particular cycle of the sterilization process failed to achieve the necessary amount of hydrogen peroxide vapor, the cycle can be repeated immediately. Strips exist to test for the presence of hydrogen peroxide but generally are poor at evaluating the level of exposure.
The present invention provides a method and device for quickly and easily determining the presence of hydrogen peroxide and more preferably the quantity of the integrated exposure to hydrogen peroxide.
A method, according to the present invention, detects the integrated exposure of hydrogen peroxide in an atmosphere. The method comprises placing a substrate capable of absorbing hydrogen peroxide into the atmosphere, contacting the substrate with the hydrogen peroxide, reacting the hydrogen peroxide with a dye intermediate and an enzyme to produce a chromophore indicative of the integrated exposure of hydrogen peroxide in the atmosphere, and correlating the chromophore to the integrated exposure of hydrogen peroxide in the atmosphere.
Preferably, the dye intermediate comprises a dye-couple of 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) and 3-dimethylaminobenzoic acid (DMAB). Also preferably, the enzyme is peroxidase.
The dye intermediate preferably comprises an oxygen acceptor, such as on of the following: O-dianisidine, O-toluidine, O-tolidine, Benzidine, 2,2xe2x80x2-Azinodi-(3-ethylbenzthiazoline sulphonic acid-(6)), 3-Methyl-2-benzothiazolinone hydrazone plus N,N-dimethylaniline, Phenyl plus 4-aminophenazone, Sulfonated 2,4-dichloro-phenol plus 4-aminophenazone, 3-Methyl-2-benzothiazolinone hydrazone plus 3-(dimethylamino)benzoic acid, 2-Methoxy-4-allyl phenol, or 4-Aminoantipyrene-dimethylaniline.
The substrate is preferably a porous receiver. The substrate can carry the dye intermediate prior to the step of contacting the substrate with the hydrogen peroxide. Alternatively, the dye intermediate can be added onto the substrate after contacting the substrate with the hydrogen peroxide.
One method of correlating the chromophore to the integrated exposure of hydrogen peroxide in the atmosphere comprises reading the chromophore with a spectrophotometer. Alternatively, it can be compared with a color chart. Similarly, the enzyme can either be on the substrate before or after contacting the substrate with hydrogen peroxide.
The substrate can be hydrated, preferably after the step of exposing the substrate to the hydrogen peroxide. A thickening agent, such as white glue, can be added to the substrate.
The aforementioned method is particularly useful in connection with the steps of removing air from the atmosphere and generating hydrogen peroxide vapor in the atmosphere.